1. Field of the Invention
The present invention relates to a copper alloy with good conductivity that is suitable for foil for the conducting members of flexible printed circuits, and particularly to copper alloy with markedly improved anisotropy and heat resistance with respect to flex durability.
2. Background Art
With the recent popularity of mobile phones, digital cameras and other compact electronic devices, demand for flexible printed circuits (FPC) has increased. Flexible printed circuits are printed circuit boards that are flexible, and being able to bend, they are often used in electronic devices that have very little extra room for mounting electronic components.
In flexible printed circuits, the circuit is typically formed from foil for the conducting members, combined with a polyimide resin or other insulating film, thus giving the circuit board itself flexibility. Examples of the circuit structure include the single-sided type, the double-sided type, the multi-layer type and various other types.
In the past, “copper foil” with low electrical resistance and good extensibility has been used for the conducting members. Specifically, a copper foil formed by rolling Tough-Pitch copper to a thickness of roughly 18-35 μm has entered the mainstream.
Various types of copper foil are recited in Patent Reference Documents 3-7 and 9 below.
On the other hand, various types of copper alloy foil have also been developed. Patent Reference Documents 1 and 2 disclose copper alloy foils for use in flexible printed circuits that contain 1% or more Zn in order to prevent the occurrence of whiskers at the time of Sn plating. Patent Reference Document 10 discloses a copper alloy foil for use in film carriers that contains Fe, P and Pb to improve the resistance to solder thermal delamination. Patent Reference Documents 11 and 12 recite copper alloy foils with Ag and Sn added for improved strength and heat resistance, and with a defined {200} plane x-ray diffraction integrated intensity for improved etching properties. In addition, Patent Reference Document 8 recites a copper alloy foil for use as the negative pole-side collector electrode material for a secondary battery, as one that selectively contains Co, Ni, Fe as well as P. Patent Reference Document 13 recites a copper alloy foil used as the electrode of a Li ion secondary battery, as one that selectively contains Fe and Ag, and contains P.
Patent Reference Document 1: JP 2-225638 A
Patent Reference Document 2: JP 3-87324 A
Patent Reference Document 3: JP 4-74837 A
Patent Reference Document 4: JP 11-286760 A
Patent Reference Document 5: JP 2000-212660 A
Patent Reference Document 6: JP 2000-256765 A
Patent Reference Document 7: JP 2001-262296 A
Patent Reference Document 8: JP 2001-279351 A
Patent Reference Document 9: JP 2003-193211 A
Patent Reference Document 10: JP 3235149 B
Patent Reference Document 11: JP 2003-96526 A
Patent Reference Document 12: JP 2003-253357 A
Patent Reference Document 13: JP 2000-328159 A